[C:1]([O:9][C:10]1[C:15](=[O:16])[N:14]2[CH2:17][CH2:18][CH2:19][CH2:20][C:13]2=[N:12][C:11]=1[C:21]([O:23][CH3:24])=[O:22])(=[O:8])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[Br:25]N1C(=O)CCC1=O.C(OOC(=O)C1C=CC=CC=1)(=O)C1C=CC=CC=1>C(Cl)(Cl)(Cl)Cl>[C:1]([O:9][C:10]1[C:15](=[O:16])[N:14]2[CH2:17][CH2:18][CH2:19][CH:20]([Br:25])[C:13]2=[N:12][C:11]=1[C:21]([O:23][CH3:24])=[O:22])(=[O:8])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1A mixture of methyl 3-(benzoyloxy)-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-2-carboxylate, N-bromo-succinimide (1.2 eq.) and dibenzoylperoxide (70%, 0.13 eq.) in carbon tetrachloride was stirred under reflux for one hour. The mixture was cooled to room temperature, the succinimide was filtered off and the solvent was removed under reduced pressure. Methyl 3-(benzoyloxy)-9-bromo-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-2-carboxylate was obtained after flash chromatography (eluent petroleum ether/ethyl acetate, 1:1) as a pale yellow oil.
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